1. Field of the Invention
The present invention relates to aircraft flight control devices, and more particularly to wing-mounted control devices. More specifically, the invention relates to an improved aileron system especially suitable for fixed-wing aircraft which provides a flight control system having improved efficiency and versatility.
2. Related Art
Immediately obvious with the invention of the airplane was the importance of controlling movement in flight, as an uncontrollable airborne airplane will soon crash. Aviators soon settled on ailerons for roll control. An aileron is a hinged panel on the trailing edge of the wing, usually located at the outboard portion of the wing, which, when deflected downwardly, increases the lift of that wing, to roll or bank the airplane into a turn. At the same time, the aileron on the other wing is deflected upwardly, to decrease the lift on that wing and thus augment the rolling motion. The configuration and application of the conventional aileron system have changed little, if at all, over more than nine decades since the first fixed-wing aircraft were produced.
One of the most objectionable features of conventional aileron application is a phenomenon known as "adverse yaw," and virtually all existing fixed-wing aircraft suffer disadvantageous consequences associated with adverse yaw. When a turn is initiated with conventional ailerons, the nose of the airplane turns first in a direction opposite to that of the intended turn. This is usually compensated by using rudder deflection to "coordinate" the turn. The adverse yawing motion is a direct result of aileron application. While producing more lift to bank the airplane into a turn, the downwardly-deflected aileron also produces more drag, which acts momentarily to cause the airplane's nose to turn in the direction opposite to the intended turn. That is, when one wing is lifted relative to the other wing by operation of a conventional aileron to bank the airplane into a turn, it is also pulled back away from the turn relative to the wing on the other side, causing the nose initially to turn, or yaw, in the direction opposite to the turn. This effect becomes increasingly detrimental as the roll rate increases and/or airspeed decreases.
Adverse yaw produced by the conventional aileron contributes to spin entry. Instinctive application of conventional ailerons during attempted spin recovery merely aggravates the spin condition. When spinning, an airplane is descending and turning in a tight spiral flight path. The conventional aileron is not effective in spin recovery. In a left hand spin, for instance, the left wing is down and toward the center of the spiral. Instinctively, many pilots are tempted to initiate right stick or control yoke movement to roll towards the right and out of the spin. With conventional ailerons this will deploy the left aileron down and the right aileron up. The left aileron will create more drag than the form drag caused by the up-going right aileron and the spin will be further aggravated. For an airplane equipped with conventional ailerons application of rudder alone is used for spin recovery. Much of spin training involves conditioning pilots to avoid the instinctive attempt to roll out of the spin. Nonetheless, many pilots have aggravated spins by attempting such recoveries with conventional ailerons.
Various methods and devices have been used to counter adverse yaw. Among them are the differential aileron with its finite deflection ratio, and the spoiler. The differential variation of conventional ailerons is the most commonly used solution and provides some marginal improvement, but has limitations. Use of spoilers may obviate adverse yaw, but spoilers present their own problems. Spoilers are so named because they spoil or effectively eliminate lift. Ailerons deliver continuously variable changes in lift within their operational envelopes, whereas spoilers operate in a step-wise manner, being functionally either on or off, and thus are difficult to modulate between full and zero effect. Roll control is difficult to achieve with spoilers without complicated sub-systems or augmenting devices.
Another disadvantage of conventional ailerons is that they also require commitment of a sizable portion of the trailing edge of the wing that could otherwise be used for beneficial high-lift devices. Such devices allow lower approach, landing and takeoff speeds, especially advantageous for heavy, high-speed commercial and high-performance military aircraft.
There are several prior-art devices which, at first glance, may appear very similar to the present invention. On closer examination, however, none of them yields the stated results or functional capabilities of this invention. Most of the previously employed devices are designed and applied as drag devices, such as ground control spoilers, drag rudders, dive brakes, or nominal flaps.
Examples of devices known in the art which are deployed upwardly to provide aircraft control may be found in the following U.S. patents:
______________________________________ 1,504,663 Wright Aug. 12, 1924 2,136,845 Fenton Nov. 15, 1938 2,138,326 Pouit Nov. 29, 1938 2,152,974 Riviere April 4, 1939 2,158,092 Taylor May 16, 1939 2,254,304 Miller Sept. 2, 1941 2,407,401 Clauser et al. Sept. 10, 1946 2,791,385 Johnson May 7, 1957 3,120,935 Perrin Feb. 11, 1964 4,717,097 Sepstrup Jan. 5, 1988 ______________________________________
Pouit describes a flap which acts more like a present-day spoiler, to prevent aircraft capsizing. In a variation, the flap has separate upper and lower elements, of which the upper element is simply hinged, and can be extended upwardly only by the upper deflection of the lower, actuated element. The upper flap member is not capable of movement independent of the lower member. Both wing flaps are operated together. Perrin describes a glider control system wherein the aileron has a secondary aileron which can be extended up to act as a drag rudder for directional yaw control in place of a rudder.
Fenton relates to a device which is basically a flap with small, subsidiary flaps on the upper and lower trailing edges. The subsidiary flaps are moved up or down through fixed, predetermined displacement, to control aircraft roll movement, with the deployment of the subsidiary flap on each side of the aircraft controlled such that when the subsidiary flap on one side is up, the corresponding subsidiary flap on the other side is down. Due to their small size, the effectiveness of the subsidiary flaps is doubtful.
Clauser et al. provides a lateral control arrangement having an airfoil member pivoted near the tip of the wing which functions as an aileron and a flap, or an "ailerflap," and a second airfoil member, or a "slot lip," pivoted above the ailerflap. Each element can pivot up and down about its neutral position. The slot lip regulates the slot spacing between the wing's trailing edge and the leading edge of the ailerflap, to alter the lift provided by the ailerflap during takeoff and landing. During flight, lateral control is achieved with the ailerflaps operated conventionally as ailerons. The slot lips move in unison with the ailerflaps, and are not capable of independent upward movement.
Johnson relates to a landing control system having a spoiler located above a conventional flap. The downwardly extending flap is used to augment lift, and the upwardly extending spoiler act as a drag plate during landing approach. The flap and spoiler on both wings are actuated simultaneously.
Miller provides a split aileron which is a combination aileron and flap. Each wing has an aileron extending almost the full span, and a flap pivoted beneath the aileron. The aileron functions conventionally, and size of the flap is limited to that of the aileron. Wright et al. describes a split flap arrangement wherein a lower element pivots down as a flap and an upper element, which pivots up and down, serves as an aileron. Riviere, Taylor and Sepstrup disclose split aileron arrangements.
Other examples of control surfaces which are formed of two, separately hinged sections and can be deployed together up and down as conventional flaps or ailerons, and are also capable of separating from each other to provide flap and air brake functions, are described in U.S. Pat. Nos. 2,427,980, 2,445,833, 2,612,329 and 2,582,348.
More recently flaperons have been employed which function both as flaps and ailerons, and offer pseudo-full-span flaps. They, however, greatly compromise the roll function and produce even greater adverse yaw than the conventional aileron when roll function is needed. Spoilers attempt to achieve objectives similar to those of the present invention, but at a great compromise in flight characteristics. Spoilers tend to have dead bands and are difficult to modulate. They, after all, "spoil" rather than modulate lift. Roll control systems involving spoilers have been used on aircraft with mixed results.
The conventional differential aileron used on most existing aircraft lessens but does not eliminate adverse yaw. It occupies a sizable portion of the wing's trailing edge, thus preventing the installation of full-span flaps. With some aircraft designs, high roll rates have been sought with the use of full-span ailerons, thus obviating entirely the installation of flaps. Other aircraft designs have sacrificed ailerons for full-span flaps, necessitating the inefficient use of tail planes or wing spoilers for roll control. No other flight control devices have the versatility or efficiency of the present invention. The Frise aileron also claims to lessen adverse yaw by deliberately creating more drag on the upwardly-deflecting aileron. This device also does not allow installation of a full-span flap.
The device closest in construction and function to the present aileron system was invented by the inventors of the present invention. Presented as the "Delta aileron" which was placed on top of a one-piece full-span flap, it has some of the features of this invention. But, it is not aerodynamically as efficient and offers less functional capability than the present invention. For example, it does not have an auxiliary flap and in its present form cannot be used as a drag rudder.